1. Field of Invention
This invention relates to desiccant containers. More specifically, this invention relates to a composition of material for use in a desiccant container comprising a combination of a deliquescent salt and a modified starch.
2. Prior Art
Desiccant containers which absorb water vapor, water, liquids and the like are well known in the art. Generally, these containers are comprised of a water or water vapor permeable packaging material formed from fibrous or film products securely sealed together at the edges of the packaging. The packaging material encapsulates a desiccant material, such as silica gel. The volume of water or water vapor absorbed by the desiccant container is generally determined by the absorbent capacity of the desiccant material contained within the container and the temperature and relative humidity level of the surrounding air.
One type of desiccant container absorbs both water vapor and liquid water by permitting both to pass through the packaging material to be absorbed by the desiccant material. In some circumstances, the packaging material for this type of product dissolves to permit the desiccant material contained within the desiccant container to have direct contact with the liquid.
Another type of desiccant container absorbs water vapor but not liquid water. The packaging material for this type of desiccant container is designed to prevent water absorbed within the desiccant container as water vapor from being released from the desiccant container in the form of liquid water.
There are many common products that are utilized as desiccating agents. Among the most common used include silica gel, calcium sulfate, calcium fluoride, activated charcoal, molecular sieves, lithium chloride, calcium chloride and other such products. A common list of drying agents is contained, for example, in Kirk-Othmer, Encyclopedia of Chemical Technology, Volume 7, pages 378-398. Common desiccating agents for use in conventional desiccant containers are also disclosed in U.S. Pat. No. 5,114,003, which discloses the use of a montmorillonite clay, silica gel, molecular sieve, calcium oxide, calcium sulfate and calcium chloride. The use of silica gel, alumino silicate, alumina, activated charcoal and molecular sieves as desiccating agents are disclosed in U.S. Pat. No. 4,464,261.
Commercial grade calcium chloride is a widely used desiccant due to its low cost and high degree of hygroscopicity. Calcium chloride compacted in the form of particles or beads is used as a drying agent, for example, in U.S. Pat. No. 3,923,944.
Mixtures and combinations of other materials have been blended with calcium chloride to form desiccating products.
For example, polyethylene glycol was mixed with calcium chloride to form a desiccant product in U.S. Pat. No. 3,779,936. In addition, U.S. Pat. No. 3,334,468 discloses the use of sodium chloride or sodium carbonate with calcium chloride. Further, the combination of calcium chloride with magnesium, lithium or ammonium salts is disclosed, for example, in U.S. Pat. No. 3,885,926. The use of calcium chloride with a metal, for example, iron fillings, is disclosed in U.S. Pat. No. 1,798,862. Further, the use of activated carbon with calcium chloride as a desiccant product is disclosed in U.S. Pat. No. 2,027,093.
U.S. Pat. No. 3,390,511 discloses the use of calcium chloride placed on a carrier material for use as a gas dryer desiccant. The preferred material that is utilized as the carrier for the calcium chloride is sodium chloride. See also, U.S. Pat. No. 3,334,468. The desiccant product in U.S. Pat. No. 3,390,511 preferably comprised about 90 to 97 percent sodium chloride as the carrier and about 10 to about 3 percent calcium chloride. In addition, sodium dichromate and trisodium phosphate in minor amounts may be included in the product. While the preferred carrier for the calcium chloride was sodium chloride, other disclosed carriers included sugar, potassium chloride, potassium nitrate, sodium nitrate and starch. See column 3, line 33. The percentage of calcium chloride used in this product was percent or less, because the major component of the product was the carrier.
One of the problems in the utilization of calcium chloride as a desiccating agent is that when the water is absorbed, it forms a liquid mixture on the surface of the calcium chloride. This is discussed in U.S. Pat. No. 3,334,468. With conventional desiccant products this liquid may leak from the packaging which can cause problems, for example, if the desiccant product is used in storage containers.
There are situations where absorption of moisture by a desiccant product even at low humidity and low water vapor pressure is necessary, such as when the product protected by the desiccant product can be damaged by moisture. Usually traditional desiccants, such as desiccant clays, silica gel, molecular sieve and calcium sulfate are used in this situation. However, for some applications the capacity for absorption of moisture of these desiccant products is too low. An example where this problem can occur is the shipment of steel products overseas. In order to avoid the rusting of these steel products, it is important that the relative humidity level in the container holding those steel products be maintained below about 40 percent at 25xc2x0 C. for as long as several weeks. While conventional desiccant products, such as silica gel, can be effective in absorbing moisture in some situations, they do not have the high capacity for absorption that is necessary for extended periods of time. Desiccant products with a higher capacity for absorption at humidity levels below 40 percent relative humidity are needed in this situation.
In other situations conventional desiccant products begin to absorb moisture at relative humidity levels which are unnecessarily low. In these situations a considerable portion of the absorption capacity of the desiccant product is wasted because moisture is absorbed at humidity levels where no damage can occur to the products being shipped with the desiccant product. In addition, if the humidity level then rises, there is a risk that these conventional desiccant products will not have sufficient remaining absorption capacity to absorb water vapor and protect the products being shipped.
In addition, it is sometimes difficult to utilize conventional desiccant products with products which inherently have a high moisture content, such as cocoa, coffee, tobacco and dog food. If the desiccant product absorbs too much moisture at relatively low humidity levels, these products may be damaged. Further, the high capacity of some desiccant products to absorb moisture is wasted in these situations. In addition, there is a risk that not enough absorption capacity will be available during the entire shipping process, especially when the humidity level rises.
While certain references disclose the use of calcium chloride and other deliquescent salts as a desiccant either alone or in combination with a number of different compositions, there is still a need for improved desiccant products utilizing calcium chloride and other deliquescent salts.
In addition, there is a need for a desiccant composition which can be useful in both low humidity and high humidity applications.
Therefore it is an object of this invention to disclose a desiccant composition containing calcium chloride and/or other deliquescent salts as its major component.
It is a still further object of this invention to disclose a desiccant composition containing calcium chloride or other deliquescent salts mixed with a significant amount of a modified starch to form the desiccant composition.
It is a still further object of the invention to disclose a desiccant composition contained within a packaging material, wherein the desiccant composition is a combination of calcium chloride or other deliquescent salts and a modified starch.
It is a still further object of this invention to disclose a desiccant composition containing calcium chloride or other deliquescent salts where water absorbed does not leak from the desiccant container.
It is a still further object of this invention to disclose a desiccant composition contained within a packaging material wherein the desiccant composition prevents leakage of water from within the package by use of a modified starch.
It is a still further object of the invention to disclose a desiccant composition contained within a packaging material which is designed for absorption of moisture in order to maintain a relatively low humidity level.
It is a still further object of the invention to disclose a desiccant composition contained within a packaging material which is designed for absorption of moisture in order to maintain a relatively high humidity level.
These and other objects and features of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description, drawings and claims. The description, along with the accompanying drawings, provides a selected example of the construction of the product and process to illustrate the invention.
In accordance with the present invention there is provided a desiccant composition comprising calcium chloride and/or other deliquescent salts and a modified starch, wherein the calcium chloride and/or other deliquescent salts comprises at least about 5 to about 95 percent of the composition by weight and the modified starch from about 5 to about 95 percent of composition. In the preferred embodiment calcium chloride and/or other deliquescent salts comprises from about 20 to about 95 percent of the composition by weight while the modified starch comprises from about 5 to about 80 percent of the composition by weight.